Oxidized alkali lignin as a rubber reinforcing agent



Patented Sept. 16, 1952 OXIDIZED ALKALI LIGNIN As AitUBBim rmmronomo gJN'r Rudolf A. V. Bali and George H. -Tomlinson, Jr., Cornwall, Ontario,Canadapassiguors .to

Howard Smith Paper.

- Quebec, Canada No Drawing.

This inventionfrelatesto v productionioflreinforced rubbers;

Application February at, 1948.1 Serial No.11 ,853 fl Claims. (01.260-175) improvements in i the I Morefparticularly," the inventionconsists m the j production of reinforced natural and/or? syn'thetio'rubbers in which thereinforcing agen consists of oxidized'alkalilignin; W v

In thepresent i' stance the invention will be described as applied tothe incorporation of oxidized'alkali lignin as a reinforcing agent in ina rubberpmasterbatch of the GR-S rubber latex type but this is merelyillustrative since the inventionfis'intended for application to thepro--' duction' ofj all types'of natural and/ or synthetic rubbers whichcan be advantageously reinforced by the incorporation therein of,oxidized alkali lignin.

It may be noted here that the above-mentioned term; GR-S is anabbreviation for Government Rubber-Type S and that this strength andresistance to rubbers reinforced typ'e-ofrubber'is an elastomer formedasa latex by tie-polymerization of an aqueous emulsion-'o'f' styrene withbutadiene under the'infiuence of a catalyst. i

Mills Limited, Montreal,

and coniferous wood lignins being in the upper range. When a: solution?of the sodium salt 'or the sodium acid salt of the alkali lignin istreated with air, the oxygen in the air reacts with the lignin and wehave found that when the lignin is precipitated with strong acid aftersuch a treatment it exhibits a higher melting point 7 thanisobtained inthe absence ofsuch an oxida f For example we have found that startingwith a lignin having a melting, point of 160 C. it is possible byregulating the amount of oxidation toproduce lignins which remaininfusible at any desiredtemperature m 1 tion treatment.-

excess of 160 C. including lignins that the infusible at 360 C.

Whereas unoxidized or only slightly oxidized lignins of a melting rangebetween 155 and 220 C. give insuflicient reinforcement of rubbers, i wehave found that it is possible to consistently V prepare reinforcedrubbers comparable in with the best grades of channel black by first Inthe alkali pulping processes, woodor other vegetable matter is digestedwith-anaqueous' alkali, the lignin and other'non cellulose organicmatter-thuspassing-into solution. The lignin maybe isolated ,by'p'recipitationfrom spent digestion liquor, commonly. known. as blackliquor, v with .acid; If a-relatively weak acid such as carbonicacidisused a product precipitates which'has'been termed the lignin acidsalt; This product, although insoluble in the presa.

ence of the inorganic salts of the carbonated black liquor, can beredissolved in hot. water. The lignin'acid salt either as such, or inaqueous solution, can be "freed of its sodium content by' treatmentwith-a strong acid such as sulfuric acid which renders it insoluble inwater, Such a product is referred to as alkali lignin. A1- tematively,the alkali lignin may be obtained directly from the spent digestionliquor by the use subjecting the lignins to be incorporated in therubber latex to an. oxidation treatment sufilcient to raise'the meltingpoint above 240 C.

This oxidation may be carried out by, bubbling dered form in a currentof hot airior oxygen. Such oxidations may be carried out in the presenceor absence of catalysts such, as the oxides of cobalt, vanadium,molybdenum, manganese; etc., or through the use of specific oxidizingThe oxidation agents such as sodium peroxide. should be continued untilthe melting point of the modified lignin, after acid precipitationanddrying, ispatleast 240 C. and preferably of the order of 300? C. or evenhigher. Concomitant with oxidation is an increase in-the viscosity ofnon-aqueous solutions, and for any given initial lignin, this propertymay'also be used as an index for adequate oxidation. A solution of theoxidized lignin acid salt orlignin salt may then be mixedwiththerubber]latex and the. lignin and rubberco-precipitate'd byacidfiication with; a strong acid such; as sulfuric or' hydrochloric"acid to which a. salt such as sodium chloride or.

alum-.can'be. added to promote coagulation.

3 Example I (1) 167 lbs. of alkali lignin from aspen wood were dissolvedin 900 lbs. of a solution containing 18 lbs. sodium peroxide. Theoxidation of this solution was carried out with air in a Rotoclone at60-70 C. for 5 hours. An amount of this solution containing 108 lbs. ofthe oxidized lignin was mixed with 768 lbs. of GR-S rubber latex,containing 2-16q1bs. of GR-S' solids. Themixture was heated to 95 C. andslowly pre-r cipitated under continuous stirring with a solution of 40lbs. of concentrated sulfuric acid and 40 lbs. sodium chloride in water.yielding a final pH of 2.5. The slurry showed a high filtering speed andcould be washed very easily. The crumb was dried, compounded and cured.The described oxidation treatment had increased the melting point of thelignin from 167 'C. to over 250 C., and the viscosity of a 10% solutionin Cellosolve from 4.24 to 4.55 cp. For purposes of comparison, masterbatches were also prepared from the original unoxidized lignin and" fromthe best grade of channel black, the former being co-precipitated asabove and the latter being'milled in; The three master batches were madeup andbompounded-in' the following proportions:

GR-S 100 1o0= 100 Original alkali lignin from aspen wood.' 50

Oxidized alkali liguin irom aspen wood E P. Channel Black.

5 owe- These samples were vulcanized at a temperature'of 145 C. and thentested, givingthe fol-- lowing results:

W00 Oxidized lignin from: coniferous wood...

fore. The results obtained were as follows:

Tensile at Break, p. s. i.

Elongation, percent Modulus Relmorcing agent used I I p. s. 1.)

Original vligrlin' from coniferous g Having thus described the nature ofthe invention with the aid of several examples, it will be understoodthat various mo difications may'be resorted to within the scope andspirit of the invention as defined by the appended claims) It willv alsobe'understood that the term rubber'f as used in'the'appended claims isto be construed] as covering both natural and synthetic rubbersto whichthe invention is applicable.

We claim:

1.'As a new a'rticle'of manufacture, a rein-' forced rubber productconsisting of butadienestyr'ene copolymer latex having incorporatedtherein a reinforcingagent consisting of oxidized alkali lignin havinga'melting point above 240 C. and'derived from plant material selectedfrom" thegroup consisti'ng'of aspen and coniferous plants. 2.As a newarticle of manufacture, arein- Iorc ed rubber productconsisting ofbutadiene-;

styrene-copolymer latex having incorporated therein a reinforcing agentconsisting of acidprecipitated, oxidized alkali lignin having. a meltingpoint above 240 C. and derived from plant I material selected from thegroupconsistingfofa gg Elonga- Modulus Reinforcing Agentuscd Break tion,(300 p s percent p. s. l.)

A.. Original alkali lignin lrom 2,230 730 500 aspen wood. 13...-Oxidized alkali lignln trom 3, 048 630 900 aspen wood. g I 0.. BestgradeoiOhannel-Black; 3, 300 675 1,085

When the sulfur in Formula B was increased to 4.0% and theCumate'reduced to 0.1%", the following values were obtained:

Tensile, p. s. i. 3375 Elongation, per cent 700' Modulus at 300%, p. s.i 334 The above described method of co-precipitation can be modified byusing different coagulants, as well as by changing the order'in whichthe reactants are added. The particle size of the crumb can becontrolled by varying "the speed of stirringand the temperature.

Example I:

(2) A sulfate liquor from coniferous wood was' treated with flue gas andheated. The separated lignin acid salt was dissolved'in hot water andthe resultant solution of" the sodium lignin salt treated 'for fourhours at 90 C. with hot'air, in

the presence of: 0.2%- of acobalt-co'ntai'nin'g aspen and coniferousplants. 3. As anew article of manufacture. a reinforced rubber productconsisting of butadienestyrene-copolymer latex having incorporatedtherein a reinforcing agent consisting of oxidized alkali lignin havinga meltin'g'point ranging from" above240- C. to 360 C. and derived fromplant material selected fromthe-group consisting of 1 aspen andconiferous'plants.

4. The method of producing a lignin-rein-' forcedbutadiene-styrene-copolymer latex which comprises subjecting a solutionof alkali lignin derived from' plant material selected fromthe groupconsisting of aspen and coniferous" plants to a-contr olled oxidizingtreatment with air to thereby raise the melting point-ofthe lignin above240 0., adding. the solution of oxidized lignin to abutadiene-styrene-copolymer latex and subjecting the resulting mixtureoflatexand lignin to the precipitating action of an acid.

' RUDOLF A. v. RAFF.

GEORGE H. romlmsoiij iii? v.1 '(References oii i'ollowiii -paie) 5 6REFERENCES CITED FOREIGN PATENTS The following references are of recordin the Number Country Date fileot this patent: 336,984 Great BritainOct. 20, 1930 UNITED STATES PATENTS 5]- OTHER REFERENCES Number NameDate Indulin, West Virginia Pulp and Paper Co.

2,140,863 Sunesson Dec. 20, 1938 2 Pages 7 433 Daly Mar. 7 Rubber Age(N- Of November, 1948, pp.

8 l 197-200. 2 1 0 Remy Aug 8 1944 10 "J. Rubber Research, Vol. 18 ofJan. 1949, pp.

1. AS A NEW ARTICLE OF MANUFACTURE, A REINFORCED RUBBER PRODUCTCONSISTING OF BUTADIENESTYRENE-COPOLYMER LATEX HAVING INCORPORATEDTHEREIN A REINFORCING AGENT CONSISTING OF OXIDIZED ALKALI LIGNIN HAVINGA MELTING POINT ABOVE 240* C. AND DERIVED FROM PLANT MATERIAL SELECTEDFROM THE GROUP CONSISTING OF ASPEN AND CONIFEROUS PLATNS.